Over the years, user interface systems of various types have been developed to facilitate control of computers and other electronic devices. Simple switches and knobs suffice to provide operator input information to some electronic devices. Computer systems, on the other hand, have generally employed more flexible data and control input means. Keyboard entry prevails in the command line environment, and the flexibility of keyboard entry dictates that some form of keyboard entry, for example, hard or soft keyboard entry, is likely to continue for the foreseeable future.
Use of pointing devices increased with the rise of graphical user interfaces. The mouse, trackball, touchpad, joystick, etc. are commonly used to direct the movement of a cursor on the display screen of a graphical user interface.
Touch screen technologies allow the surface or near surface of a display to serve as a user interface device. The touch screen detects user input in the form of screen touches, or near screen touches when using some touch screen technologies. Touch screens are advantageous in that no dedicated input device, apart from the touch detection apparatus coupled to the display, is required. A variety of touch screen technologies are available, including resistive, capacitive, infra-red, surface acoustic wave, and video each with its advantages and disadvantages.
Touch screen systems enabling recognition of multiple touch points have become increasingly popular. These systems, allow the use of gestures (e.g., hand or finger motion) and/or chording (e.g., the simultaneous use of multiple finger or hand touch points) to extend and simplify touch screen operations. However, like a large vocabulary of commands in a command line system, an extensive set of gestures may be difficult for a user to remember. Moreover, many conceivable gestures may entail unnatural movements.